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Publication Number: FHWA-HRT-06-033
Date: August 2006

Task Analysis of Intersection Driving Scenarios: Information Processing Bottlenecks

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Scenario 6–Right turn on Red Light

Description

This scenario involves the subject vehicle making a right turn on a red light after changing lanes to get into the right lane. Figure 45 shows the scenario diagram and provides additional details regarding the scenario. Briefly described, this scenario involves the subject driver identifying the intersection as the turn location and then the driver quickly changes lanes to get into the correct turn lane before decelerating to a stop at the intersection. Following this action, the subject driver advances into the crosswalk to get a better view of oncoming right-traveling traffic and waits until it is safe to go before executing the turn.

This scenario was divided into six segments (Approach, Prepare for Lane Change, Execute Lane Change, Stop, Prepare for Turn/Intersection Entry, and Execute Turn). The primary bases for parsing the scenario into these particular segments were that each segment had a different overall driving goal and most segments had different speed characteristics (table 65).

Table 65. Scenario 6–Right Turn on Red Light driving objectives and speed characteristics for each scenario segment as a basis for the scenario partitioning.

Segment

Driving Objectives

Speed Characteristics

Approach

Identify upcoming intersection as the location of the turn.

Traveling at full speed.

Prepare for Lane Change

Determine if a lane change is feasible/safe.

Traveling near full speed.

Execute Lane Change

Maneuver into right lane.

Traveling near full speed with speed adjustments.

Stop

Stop at the intersection.

Controlled deceleration.

Prepare for Turn/ Intersection Entry

Get into position to turn. Decide that it is safe to turn.

Slow advance into position.

Execute turn

Make the turn.

Turning and accelerating up to speed.

The relevant crash data for this scenario involving lane changes and right turns are discussed in Scenario 4–Straight on Green Light and Scenario 5–Right Turn on Green Light. The key problems for lane changes are that the tasks associated with determining whether it is safe to change lanes in the Prepare for Lane Change segment appear to be performance bottlenecks, especially with the inherent time limitations created by the approaching intersection. In addition, the relative prevalence of driver distraction, but not visual obstruction, in right-turn crashes suggests that the cognitive subtasks in the Intersection Entry segment are likely to be primary sources of difficulty during the preparation for the turn.

Figure 45 shows the Scenario 6 diagram and lists the details.

Scenario 6 Diagram

View Alternative Text

  • Segments are demarked by dotted lines.
  • Approximate speed in km/h is indicated on the right.

Note: Illustration dimensions and vehicle positions are not to scale.

Figure 45. Scenario 6–Right Turn on Red Light scenario diagram, details, and assumptions.


Scenario Details

Activity:

Right Turn on a Red Light

Scenario Segments:

  • Approach
  • Prepare for Lane Change
  • Execute Lane Change
  • Stop
  • Prepare for Turn/Intersection Entry
  • Execute Turn

Intersection Configuration:

  • Four-lane urban signalized intersection without a dedicated left-turn lane or a left-turn signal.

Traffic Volume:

  • Moderate (driving speeds are at speed limit and other lead/following/adjacent vehicles are present).

Assumptions/Complicating Factors:

  • The turn intersection is familiar to the subject vehicle driver.
  • There are no following or lead vehicles in the subject vehicle's originating lane.
  • The driver must change lanes to get into the turning lane.
  • There is a following vehicle in the destination lane but no lead vehicle.
  • There are right-traveling vehicles in both the inside and outside lanes.

Several assumptions were made regarding the situational aspects of the scenario. The justifications for these are summarized in figure 45 and more fully described in table 66.

Table 66. Scenario 6–Right Turn on Red Light assumptions and corresponding justifications.

Assumption

Justification

The turn intersection is familiar to the subject vehicle driver.

The driver simply has to recognize the intersection as the correct turn intersection, which provides some variation from other scenarios.

There are no following or lead vehicles in the subject vehicle's originating lane.

This situation provides some variety across scenarios.

The driver must change lanes to get into the turning lane.

This situation increases the difficulty of this scenario.

There is a following vehicle in the destination lane but no lead vehicle.

This situation increases the difficulty of the lane-change-related activities and it also provides some variation from the lane change conditions in Scenario 4.

There are right-traveling vehicles in both the inside and outside lanes.

This situation makes the gap judgments and turn execution more difficult by requiring the subject driver to check for potential conflicts with drivers in both right-traveling lanes.

Scenario Timeline

An approximate timeline showing the key temporal milestones for Scenario 6 was calculated based on vehicle kinematics (figure 46). These milestones were used to make judgments about the pacing of tasks within segments and to provide a basis for the overall sequencing of certain tasks. Some segments included an interval with a variable time component, which represented intervals that were either long enough to effectively provide unlimited time to perform tasks or of a duration that was determined external to vehicle kinematic factors (e.g., waiting for lead vehicle to turn).

View Alternative Text

Figure 46. Scenario 6–Right Turn on Red Light Scenario

timeline depicting key segment phases duration and event/task milestones.

Task Analysis Table

The results of the task analysis organized by scenario segment are shown in the task analysis table (table 67). The task analysis results are duplicated for individual segments in the segment analyses tables in next sections, which also more fully discuss the organization and content of the tasks and information processing subtasks.

Table 67. Scenario 6–Right Turn on Red Light task analysis table.

Task

Perceptual Subtasks

Cognitive Subtasks

Psychomotor Subtasks

6.1 Approach

6.1.1. Maintain safe lane position.

Visually observe roadway ahead.

Verify correct lane position.

Make necessary adjustments to steering.

6.1.2. Check surround for unsafe situations.

Scan for potential obstacles/hazards.
Listen for indications of unsafe situations.

Determine whether perceptual input indicates if current situation is safe/unsafe.

Head and eye movements for scanning.

6.1.3. Decelerate.

Visually assess distance to intersection.

Determine when vehicle is close enough to intersection to begin deceleration.

Coast (foot off accelerator) and/or gentle braking.

6.1.4. Identify intersection as correct turn intersection.

View visual scene for indicator landmarks or street signs.

Recognize familiar intersection as correct turn intersection.

Head and eye movements for scanning.

6.1.5. Identify intersection characteristics.

Visually identify lane configurations, pavement marking and signs, signal location, etc.

Determine if any nonroutine actions are required.

Head and eye movements for scanning.

6.1.6. Observe status of light.

Visually observe traffic signal.

Identify color/status of traffic light.

Head and eye movements to view traffic signal.

6.2. Prepare for Lane Change

6.2.1. Maintain safe lane position.

Visually observe roadway ahead.

Verify correct lane position.

Make necessary adjustments to steering.

6.2.2. Check surround for unsafe situations.

Scan for potential obstacles/hazards.
Listen for indications of unsafe situations.

Determine whether perceptual input indicates if current situation is safe/unsafe.

Head and eye movements for scanning.

6.2.3. Decide whether lane change is legally permissible (e.g., lane markings are not solid).

Scan for signs prohibiting lane change.

Visually observe pavement markings.

Make yes/no decision regarding legality based on observed information.

Head and eye movements to look for indicators.

6.2.4. Confirm that there is no lead vehicle in right lane.

View right lane.

Identify if any lead vehicles are present in the right lane.

Head and eye movements for viewing right lane.

6.2.5. Check rearview mirror for rear-approaching traffic.

Observe presence and relative speed of rear-approaching traffic.

Determine if there will be a potential conflict with rear-approaching traffic.

Head and eye movements to observe rearview mirror.

6.2.6. Check blind spot for rear-approaching traffic in right lane.

Visually observe right lane over shoulder.

Identify if any vehicles are present.

Head and eye movements to perform shoulder check.

6.3. Execute Lane Change

6.3.1. Check surround for unsafe situations.

Scan for potential obstacles/hazards
Listen for indications of unsafe situations.

Determine whether perceptual input indicates if current situation is safe/unsafe.

Head and eye movements for scanning.

6.3.2. Activate turn signal.

Locate the control (automatic behavior).

Identify which direction to activate the control (automatic behavior).

Activate turn signal control.

6.3.3. Adjust vehicle speed to avoid conflicts with right-lane following vehicle traveling at constant speed.

Visually assess distance and relative speed of following vehicle in right lane.

Determine if distance and relative speed are safe.

Accelerate if necessary.
Head and eye movements to view vehicle.

6.3.4. Change lane.

Visually observe vehicle lateral position.

Identify when vehicle is completely in new lane.

Steer into new lane and adjust vehicle position.

6.4. Stop

6.4.1. Maintain safe lane position.

Visually observe roadway ahead.

Verify correct lane position.

Make necessary adjustments to steering.

6.4.2. Check surround for unsafe situations.

Scan for potential obstacles/hazards.
Listen for indications of unsafe situations.

Determine whether perceptual input indicates if current situation is safe/unsafe.

Head and eye movements for scanning.

6.4.3. Maintain safe distance from decelerating following vehicle.

Visually assess distance and relative speed of following vehicle.

Determine if following-vehicle closing trajectory is safe.

Reduce deceleration if necessary.
Head and eye movements to observe rearview mirror.

6.4.4. Activate turn signal.

Visually assess distance to intersection.

Recognize that the vehicle is close enough to intersection to start signaling.

Activate turn signal control.

6.4.5. Begin deceleration.

Visually assess distance to intersection.

Recognize that the vehicle is close enough to intersection to begin deceleration.

Coast (foot off accelerator) and/or initiate braking.

6.4.6. Observe vehicle stopping trajectory.

Visually assess distance to intersection.

Determine if deceleration rate will lead to safely stopping at stop line.

Make necessary adjustments to deceleration rate.

6.4.7. Observe status of light.

Visually observe traffic signal.

Identify color/status of traffic light.

Head and eye movements to view traffic signal.

6.4.8. Stop.

Visually assess distance to stop line.

Identify when stop line is reached.

Fully press and hold brake.

6.5. Prepare for Turn /Intersection Entry

6.5.1. Check for conflicts with following vehicle.

Visually assess trajectory of following vehicle.

Determine if distance and speed of following vehicle indicate potential conflict.

Head and eye movements to observe rearview mirror.

6.5.2. Make sure pedestrians/cyclists are not crossing or about to cross.

Look left and right along crosswalk.

Identify if pedestrians/cyclists are present.

Head and eye movements for viewing.

6.5.3. Observe status of light.

Visually observe traffic signal.

Identify color/status of traffic light.

Head and eye movements to view traffic signal.

6.5.4. Advance into the crosswalk.

Visually observe crosswalk.

Determine when vehicle is at an appropriate position for turning.

Slowly accelerate and brake.

6.5.5. Look for gap in right-going traffic.

Visually monitor traffic.

Determine distance and speed of oncoming traffic.
Determine if there is a gap sufficient for turning.

Head and eye movements to monitor oncoming traffic.

6.5.6. Check for right-traveling vehicles in inside lane changing to outside (conflicting) lane.

Monitor oncoming vehicles in inside lane.

Determine if vehicle is about to change lanes (e.g., turn signal on).

Head and eye movements to monitor oncoming traffic.

6.5.7. Check for hazards in turn path.

Visually scan turn path to the right and intended lane (especially crosswalk).

Determine if any pedestrians/cyclists or other hazards are in the crosswalk or about to enter.

Head and eye movements to view right-turn path.

6.6. Execute Turn

6.6.1. Accelerate to initiate turn.

View roadway to right.

Determine that acceleration is sufficient to get vehicle through the intersection in a timely manner.

Accelerate at necessary rate.
Head and eye movements to view roadway.

6.6.2. Steer into turn.

View turn path.

Determine that vehicle trajectory and lane position are appropriate.

Steer to the right and make necessary adjustments to stay in lane.

6.6.3.Check for hazards in turn path.

Visually scan turn path to the right and intended lane (especially crosswalk).

Determine if any pedestrians/cyclists or other hazards are in the crosswalk or about to enter.

Head and eye movements to view right-turn path.

6.6.4. Check for conflicts with vehicle in inside lane.

Visually assess trajectory of vehicle.

Determine if distance and trajectory are safe.

Confirm that vehicle does not try to cut into lane.

Head and eye movements to view vehicle.
Adjust speed if necessary.

6.6.5. Continue accelerating up to speed.

Visually observe roadway.

Determine when traveling speed reached.

Accelerate at needed rate.
Head and eye movements for viewing.

6.6.6. Maintain safe lane position.

Visually observe roadway ahead.

Verify correct lane position.

Make necessary adjustments to steering.

6.6.7. Check surround for unsafe situations.

Scan for potential obstacles/hazards.
Listen for indications of unsafe situations.

Determine whether perceptual input indicates if current situation is safe/unsafe.

Head and eye movements for scanning.

6.6.8. Maintain safe distance from following vehicle at constant speed.

Visually assess distance and relative speed of following vehicle.

Determine if following-vehicle closing trajectory is safe.

Increase acceleration if necessary.
Head and eye movements to observe rearview mirror.

Segment Analysis

Scenario 6, Segment 1, Approach

The Approach segment involves the subject vehicle traveling at full speed until the intersection is identified as the turn intersection and the driver determines that a lane change is required to get into the turning lane. The tasks, information processing subtasks, and workload estimates associated with this segment are shown in table 68. The scenario diagram, relative timing of tasks, and potential contributions to information processing bottlenecks and mitigating factors are shown in figure 47 and table 69.

Table 68. Scenario 6–Right Turn on Red Light Approach segment

tasks and information processing subtasks.

Task

Perceptual Subtasks

Cognitive Subtasks

Psychomotor Subtasks

6.1.1 Maintain safe lane position.

Visually observe roadway ahead.

1

Verify correct lane position.

1

Make necessary adjustments to steering.

1

6.1.2 Check surround for unsafe situations.

Scan for potential obstacles/hazards.
Listen for indications of unsafe situations.

7

Determine whether perceptual input indicates if current situation is safe/unsafe.

4

Head and eye movements for scanning.

1

6.1.3 Decelerate.

Visually assess distance to intersection.

4

Determine when vehicle is close enough to intersection to begin deceleration.

6

Coast (foot off accelerator) and/or gentle braking.

3

6.1.4 Identify intersection as correct turn intersection.

View visual scene for indicator landmarks or street signs.

3

Recognize familiar intersection as correct turn intersection.

3

Head and eye movements for scanning.

1

6.1.5 Identify intersection characteristics.

Visually identify lane configurations, pavement marking and signs, signal location, etc.

6

Determine if any nonroutine actions are required.

6

Head and eye movements for scanning.

1

6.1.6 Observe status of light.

Visually observe traffic signal.

2

Identify color/status of traffic light.

2

Head and eye movements to view traffic signal.

1

Several aspects of the task analysis and workload estimates warrant discussion. The first is that the deceleration that takes place in task 6.1.3 (decelerate) is not the same as the deceleration in the Stop segment (6.4), which stops the vehicle. Instead, the task 6.1.3 deceleration is just general deceleration that should be part of any approach to an intersection.(9) In addition, task 6.1.4 (identify intersection as turn intersection) is not directly specified in the task analysis references used,(9) but is instead included because logically it is a necessary part of this segment. Also, no task for activating the turn signal is defined in this segment because the subject vehicle must first change lanes (covered in the next two segments) before making the turn.

Another noteworthy point is that for this scenario the subject driver is familiar with the intersection. Here, the visual and cognitive demands are reduced because a direct search is not necessary to recognize the intersection.

Scenario 6, Segment 1 Diagram

View Alternative Text

Blue dotted outlines indicate general distribution of primary information in key perceptual tasks.

Note: Illustration dimensions and vehicle positions are not to scale.

Figure 47. Scenario 6–Right Turn on Red Light Approach segment scenario diagram.


Table 69 Scenario 6–Right Turn on Red Light Approach segment relative timing and duration of segment tasks and summary of key findings.

View Alternative Text

Potential contributions to high workload and information processing bottlenecks:

  • Some perceptual tasks involving scanning in 6.1.2 and 6.1.5.
  • Some cognitive tasks involving evaluation or judgment of multiple factors in 6.1.4 and 6.1.5.

Mitigating factors:

  • Most of the tasks are self-paced.
  • Most of the tasks are routine, automatic activities.

Task Pacing and Timing - Task 6.1.1 (lane maintenance) is forced-paced because it is part of the ongoing task of driving, but the other tasks are self-paced.

In the task ordering, tasks 6.1.3 through 6.1.6 are sequential and can be performed in any order. The ordering chosen in this segment followed a logical sequence and was consistent with the ordering of similar tasks in the Approach segments in other driving scenarios included in this effort.

Scenario 6, Segment 2, Prepare for Lane Change

The Prepare for Lane Change segment spans the time from when the subject driver determines that a lane change is required and gets into the turning lane to when the driver decides that it is legal and safe to make a lane change. The tasks, information processing subtasks, and workload estimates associated with this segment are shown in table 70. The scenario diagram, relative timing of tasks, and potential contributions to information processing bottlenecks and mitigating factors are shown in figure 48 and table 71.

Table 70. Scenario 6–Right Turn on Red Light Prepare for Lane Change segment

tasks and information processing subtasks.

Task

Perceptual Subtasks

Cognitive Subtasks

Psychomotor Subtasks

6.2.1 Maintain safe lane position.

Visually observe roadway ahead.

1

Verify correct lane position.

1

Make necessary adjustments to steering.

1

6.2.2 Check surround for unsafe situations.

Scan for potential obstacles/hazards.
Listen for indications of unsafe situations.

7

Determine whether perceptual input indicates if current situation is safe/unsafe.

4

Head and eye movements for scanning.

1

6.2.3 Decide whether lane change is legally permissible (e.g., lane markings are not solid).

Scan for signs prohibiting lane change.
Visually observe pavement markings.

7

Interpret information regarding legality based on observed information.

5

Head and eye movements for looking for indicators.

1

6.2.4 Confirm that there is no lead vehicle in right lane.

View right lane.

3

Identify if any lead vehicles are present in the right lane.

2

Head and eye movements for viewing right lane.

3

6.2.5 Check rearview mirror for rear-approaching traffic.

Observe presence and relative speed of rear-approaching traffic.

4

Determine if there will be a potential conflict with rear-approaching traffic.*

5

Head and eye movements to observe rearview mirror.

1

6.2.6 Check blind spot for rear-approaching traffic in right lane.

Visually observe right lane over shoulder.

1

Identify if any vehicles are present.

2

Head and eye movements to observe and perform shoulder check.

1

* Difficulty in this subtask is increased by a value of 1 because of degraded information.

Several points about the task analysis and workload estimation warrant discussion. First is the assumption that there is a vehicle behind the subject vehicle in the right destination lane but no vehicle in front. This assumption increases the level of difficulty to the lane-change maneuver while providing some variety from Scenario 4, which had both lead and following vehicles. Consequently, task 6.2.4 (confirm that there is no lead vehicle in right lane) is easier to conduct than if the scenario included a lead vehicle but still must be performed because it is necessary to confirm that there is indeed no lead vehicle in the way. Another notable point is that there is no separate task defined for the actual decision about whether or not to change lanes. This decision process is the culmination of tasks (6.2.3 through 6.2.6) and the assumption is that the decision is an implicit result of resolving these tasks. Finally, the workload value of the task 6.2.5 (check rearview mirror for rear-approaching traffic) cognitive element was incremented by 1 because this task is made more difficult with the degraded indirect visual information from the rearview mirror.

Scenario 6, Segment 2 Diagram

View Alternative Text

Blue dotted outlines indicate general distribution of primary information in key perceptual tasks.

Note: Illustration dimensions and vehicle positions are not to scale.

Figure 48. Scenario 6–Right Turn on Red Light Prepare for Lane Change segment of scenario diagram.


Table 71. Scenario 6–Right Turn on Red Light Prepare for Lane Change segment of relative timing and duration of segment tasks and summary of key findings.

View Alternative Text

Potential contributions to high workload and information processing bottlenecks:

  • Perceptual tasks involving scanning in 6.2.2 and 6.2.3.
  • Cognitive tasks involving interpretation of information in 6.2.3 and evaluation of a single factor under difficult conditions in 6.2.5.
  • Tasks 6.2.3 through 6.2.6 are forced-paced and must be completed in a relatively short period of time.

Mitigating factors:

  • None.

Task Pacing and Timing - Task 6.2.1 (lane maintenance) is forced-paced because it is part of the ongoing task of driving. Tasks 6.2.3 through 6.2.6 are forced-paced because they must be completed before initiating the lane change, which is itself constrained by the approaching intersection.

Regarding the task ordering, tasks 6.2.2 through 6.2.6 are shown as overlapping sequential tasks that follow the sequence described in the McKnight and Adams (1970) task analysis.(9) The reason for presenting them this way is that these tasks all involve visual information acquisition (which can only be done in sequence) that requires precise yet rapid deployment of visual gaze and attention to distributed locations throughout the visual scene. Consequently, there is likely to be some interference between these sequential tasks; however, because more time is available than in other time-limited segments with task interference (e.g., Decision to Proceed in scenario 3), the overlap was limited to adjacent tasks, rather than making them all simultaneous.

Scenario 6, Segment 3, Execute Lane Change

The Execute Lane Change segment spans from the time that the subject vehicle initiates the lane change until the vehicle is established in the new lane. The tasks, information processing subtasks, and workload estimates associated with this segment are shown in table 72, and the scenario diagram, relative timing of tasks, and potential contributions to information processing bottlenecks and mitigating factors are shown in figure 49 and table 73.

Table 72. Scenario 6–Right Turn on Red Light Execute Lane Change segment

tasks and information processing subtasks.

Task

Perceptual Subtasks

Cognitive Subtasks

Psychomotor Subtasks

6.3.1 Check surround for unsafe situations.

Scan for potential obstacles/hazards.
Listen for indications of unsafe situations.

7

Determine whether perceptual input indicates if current situation is safe/unsafe.

4

Head and eye movements for scanning.

1

6.3.2 Activate turn signal.

Locate the control (automatic behavior).

1

Identify which direction to activate the control (automatic behavior).

1

Activate turn signal control.

1

6.3.3 Adjust vehicle speed to avoid conflicts with right-lane following vehicle traveling at constant speed.

Visually assess distance and relative speed of following vehicle in right lane.

4

Determine if distance and relative speed are safe.*

7

Accelerate if necessary.
Head and eye movements to view vehicle.

3

6.3.4 Change lane.

Visually observe vehicle lateral position.

1

Identify when vehicle is completely in new lane.

2

Steer into new lane and adjust vehicle position.

3

* Difficulty in this subtask is increased by a value of 1 because of degraded information.

Several points about the task analysis and workload estimation warrant discussion. The first point is that task 6.3.2 (activate turn signal) was included in this segment because it should be done after determining that it is legal and safe to change lanes. Although it could have been included in the previous segment, it was included in this segment largely because research indicates that, in practice, many drivers do not activate the turn signal until the lane change is underway.(25) Also, the turn signal activation workload demands were assigned minimum values (workload = 1) because this is a highly learned automatic activity. Another point is that the maintain safe lane position task was not included in this segment because the subject vehicle is changing lanes during this segment. Finally, the estimated workload value for the task 6.3.3 cognitive element was incremented by a value of 1, because determining if the relative speed and distance of the following vehicle are safe is more difficult to do using the degraded indirect visual information from the rearview mirror.

Scenario 6, Segment 3 Diagram

View Alternative Text

Blue dotted outlines indicate general distribution of primary information in key perceptual task.

Note: Illustration dimensions and vehicle positions are not to scale.

Figure 49. Scenario 6–Right Turn on Red Light Execute Lane Change segment diagram.


Table 73. Scenario 6–Right Turn on Red Light Execute Lane Change segment of relative timing and duration of segment tasks and summary of key findings.

View Alternative Text

Potential contributions to high workload and information processing bottlenecks:

  • Tasks 6.3.2 through 6.3.4 are forced-paced and must be completed in a relatively short period of time.

Mitigating factors:

  • Most of the tasks are routine.

 

Task Pacing and Timing - Tasks 6.3.2 through 6.3.4 are forced-paced because they must be completed before the subject vehicle gets too close to the intersection.

In the task ordering, task 6.3.2 (activate the turn signal) initiates the segment, whereas task 6.3.3 (adjust vehicle speed to avoid conflicts with decelerating right-lane following vehicle) is ongoing both before and during the actual lane-change maneuver (task 6.3.4).

Scenario 6, Segment 4, Stop

The Stop segment ranges from when the subject vehicle begins to decelerate after establishing itself in the new lane until the vehicle comes to a complete stop at the stop line. The tasks, information processing subtasks, and workload estimates associated with this segment are shown in table 74. The scenario diagram, relative timing of tasks, and potential contributions to information processing bottlenecks and mitigating factors are shown in figure 50 and table 75.

Table 74. Stop Segment of Scenario 6–Right Turn on Red Light

tasks and information processing subtasks.

Task

Perceptual Subtasks

Cognitive Subtasks

Psychomotor Subtasks

6.4.1 Maintain safe lane position.

Visually observe roadway ahead.

1

Verify correct lane position.

1

Make necessary adjustments to steering.

1

6.4.2 Check surround for unsafe situations.

Scan for potential obstacles/hazards.

Listen for indications of unsafe situations.

7

Determine whether perceptual input indicates if current situation is safe/unsafe.

4

Head and eye movements for scanning.

1

6.4.3 Maintain safe distance from decelerating following vehicle.

Visually assess distance and relative speed of following vehicle.

4

Determine if following-vehicle closing trajectory is safe.*

5

Reduce deceleration if necessary.

Head and eye movements to observe rearview mirror.

3

6.4.4 Activate turn signal.

Visually assess distance to intersection.

4

Recognize that the vehicle is close enough to intersection to start signaling.

3

Activate turn signal control.

2

6.4.5 Begin deceleration.

Visually assess distance to intersection.

4

Recognize that the vehicle is close enough to intersection to begin deceleration.

3

Coast (foot off accelerator) and/or initiate braking.

3

6.4.6 Observe vehicle stopping trajectory.

Visually assess distance to intersection.

4

Determine if deceleration rate will lead to safely stopping at stop line.

6

Make necessary adjustments to deceleration rate.

3

6.4.7 Observe status of light.

Visually observe traffic signal.

2

Identify color/status of traffic light.

2

Head and eye movements to view traffic signal.

1

6.4.8 Stop.

Visually assess distance to stop line.

4

Identify when stop line reached.

2

Fully press and hold brake.

2

* Difficulty in this subtask is increased by a value of 1 because of degraded information.

One assumption in this segment is that the subject vehicle is far enough away from the intersection that deceleration does not have to start until the lane change is complete. Also, task 6.4.4 (activate turn signal) may be unnecessary if the subject vehicle's signal did not automatically cancel following the lane change; however, this task was included to cover the situation in which it does cancel, and, more importantly, because the signal activation has a different purpose than in the previous segment. (signal for lane change versus signal for intersection turn). Also a simplified version of tasks 6.4.4 and 6.4.5 (begin deceleration) cognitive elements was assumed because by the time the subject vehicle completes the lane change, it is close enough to the intersection that it should be obvious that it is time to signal and decelerate at an aggressive rate (appendix A). Finally, the estimated workload value for the task 6.4.3 cognitive subtask was incremented by a value of 1, because determining if the relative speed and distance of the following vehicle are safe is more difficult to do using the degraded indirect visual information from the rearview mirror.

Scenario 6, Segment 4 Diagram

View Alternative Text

Blue dotted outlines indicate general distribution of primary information in key perceptual tasks.

Note: Illustration dimensions and vehicle positions are not to scale.

Figure 50. Scenario 6–Right Turn on Red Light Stop segment diagram.

Table 75. Scenario 6–Right Turn on Red Light Stop segment of relative timing and duration of segment tasks and summary of key findings.

View Alternative Text

Potential contributions to high workload and information processing bottlenecks:

  • Concurrent and continuous conduct of 6.4.1, 6.4.2, 6.4.3, and 6.4.6.
  • Several demanding cognitive tasks involving either evaluation or judgment of multiple simultaneous factors (6.5.5 and 6.5.6) or a single factor under increased difficulty (6.5.3).
  • A high number of tasks overall.

Mitigating factors:

  • Most of the difficult tasks are self-paced.
  • Several tasks are routine, automatic activities.

Task Pacing and Timing - Task 6.4.1 (lane maintenance) is forced-paced because it is part of the ongoing task of driving. Also, tasks 6.4.4 (activate turn signal) and 6.4.5 (begin decelerating) are forced-paced because the intersection is rapidly approaching, and task 6.4.8 (stop) is forced-paced because the subject vehicle has to stop behind the stop line.

Regarding the task ordering, tasks 6.4.4 (activate turn signal) and 6.4.5 (begin decelerating) occur immediately and concurrently because the subject driver needs to start decelerating immediately and should signal the intention to turn as soon as possible. The next tasks-6.4.6 (observe stopping trajectory), and 6.4.8 (stop)-follow an obvious sequence, while the other tasks are essentially ongoing throughout the segment. The exception is task 6.4.7 (observe status of light), which is temporally discrete and can occur over a range of time.

Scenario 6, Segment 5, Prepare for Turn/Intersection Entry

The Prepare for Turn/Intersection Entry segment involves the subject vehicle advancing into the crosswalk to get a better view of right-traveling traffic when it is safe to do so, and then monitoring traffic until there is a sufficient gap to make the right turn. The tasks, information processing subtasks, and workload estimates associated with this segment are shown in table 76. The scenario diagram, relative timing of tasks, and potential contributions to information processing bottlenecks and mitigating factors are shown in figure 51 and table 77.

Table 76. Scenario 6–Right Turn on Red Light Prepare for Turn/Intersection Entry segment tasks and information processing subtasks.

Task

Perceptual Subtasks

Cognitive Subtasks

Psychomotor Subtasks

6.5.1 Check for conflicts with following vehicle.

Visually assess trajectory of following vehicle.

4

Determine if distance and speed of following vehicle indicate potential conflict.*

5

Head and eye movements to observe rearview mirror.

1

6.5.2 Make sure pedestrians/cyclists are not crossing or about to cross.

Look left and right along crosswalk.

3

Identify if pedestrians/cyclists are present.

2

Head and eye movements for viewing.

1

6.5.3 Observe status of light.

Visually observe traffic signal.

2

Identify color/status of traffic light.

2

Head and eye movements to view traffic signal.

1

6.5.4 Advance into the crosswalk.

Visually observe crosswalk.

1

Determine when vehicle is in an appropriate position for turning.

4

Slowly accelerate and brake.

3

6.5.5 Look for gap in right-going traffic.

Visually monitor traffic.

5

Determine distance and speed of oncoming traffic.

Determine if there is a gap sufficient for turning.

6

Head and eye movements to monitor oncoming traffic.

1

6.5.6 Check for right-traveling vehicles in inside lane changing to outside (conflicting) lane.

Monitor oncoming vehicles in inside lane.

5

Determine if vehicle is about to change lanes (e.g., turn signal on).

6

Head and eye movements to monitor oncoming traffic.

1

6.5.7 Check for hazards in turn path.

Visually scan turn path to the right and intended lane (especially crosswalk).

7

Determine if any pedestrians/cyclists or other hazards are in the crosswalk or about to enter.

4

Head and eye movements to view right-turn path.

1

* Difficulty in this subtask is increased by a value of 1 because of degraded information.

Task 6.5.3 (observe status of the light) is included for two reasons: Drivers need to know the traffic signal status to maintain awareness of the current situation and pedestrian/cyclist behavior may change depending on the light status (e.g., some pedestrians may run out into the crosswalk if the light is about to turn yellow in order to try to make it across at the last minute). Also note that there is no separate task defined for the actual decision regarding whether it is safe to turn. This decision process is the culmination of tasks 6.5.5 through 6.5.7, and the assumption is that the decision is an implicit result of resolving these tasks. Finally, the estimated workload value for the task 6.5.1 cognitive subtask was incremented by a value of 1, because determining the trajectory of the following vehicle is more difficult to do using the degraded indirect visual information from the rearview mirror.

Scenario 6, Segment 5 Diagram

View Alternative Text

Blue dotted outlines indicate general distribution of primary information in key perceptual tasks.

Note: Illustration dimensions and vehicle positions are not to scale.

Figure 51. Scenario 6–Right Turn on Red Light Prepare for Turn/Intersection Entry segment of scenario diagram.

Table 77. Scenario 6–Right Turn on Red Light Prepare for Turn / Intersection Entry segment relative timing and duration of segment tasks and summary of key findings.

View Alternative Text

Potential contributions to high workload and information processing bottlenecks:

  • Concurrent and continuous conduct of 6.5.1, 6.5.5, 6.5.6, and 6.5.7 under high time pressure.
  • The majority of the time in this segment is likely to be taken by forced-paced tasks that have relatively high perceptual workload (6.5.5, 6.5.6, and 6.5.7) and/or high cognitive workload (6.5.5 and 6.5.6).
  • Task 6.5.6 represents a high-stress decision with possible severe consequences if done inaccurately.
Mitigating factors:
  • Initial tasks are self-paced.

Task Pacing and Timing - Tasks 6.5.5 through 6.5.7 are forced-paced because the subject driver is limited in time because new gaps are continuously appearing and requiring evaluation, forcing the driver back to task 6.5.5 (look for gap in traffic). This step repeats until a safe gap is finally identified, then the driver is limited in time because the gap is rapidly approaching and the decision to turn must be completed before the lead safe-gap vehicle arrives at the intersection.

In the task ordering, task 6.5.2 (check for conflicts with following vehicle) is ongoing throughout the segment. Tasks 6.5.5 through 6.5.7 are concurrent because the driver must repeatedly cycle between evaluating new gaps as they become visible (task 6.5.2) and maintaining a current assessment of the situation (tasks 6.5.1, 6.5.6, and 6.5.7). The other tasks were ordered based on logical sequence: note that this sequence has no effect on combined or average workload levels because the tasks are all sequential.

Scenario 6, Segment 6, Execute Turn

The Execute Turn segment involves the actions related to initiating and completing the right turn (it was determined in segment 5 that it was safe to turn) and getting up to speed in the new lane. The tasks, information processing subtasks, and workload estimates associated with this segment are shown in table 78. The scenario diagram, relative timing of tasks, and potential contributions to information processing bottlenecks and mitigating factors are shown in figure 52 and table 79.

Table 78. Scenario 6–Right Turn on Red Light Execute Turn segment

tasks and information processing subtasks.

Task

Perceptual Subtasks

Cognitive Subtasks

Psychomotor Subtasks

6.6.1 Accelerate to initiate turn and get up to speed.

View roadway to right.

3

Determine that acceleration is sufficient to get vehicle through the intersection in a timely manner.

4

Accelerate at necessary rate.
Head and eye movements to view roadway.

3

6.6.2 Steer into turn.

View turn path.

3

Determine that vehicle trajectory and lane position are appropriate.

6

Steer to the right and make necessary adjustments to stay in lane.

3

6.6.3 Check for hazards in turn path.

Visually scan turn path to the right and intended lane (especially crosswalk).

7

Determine if any pedestrians/cyclists or other hazards are in the crosswalk or about to enter.

4

Head and eye movements to view right-turn path.

1

6.6.4 Check for conflicts with vehicle in inside lane.

Visually assess trajectory of vehicle.

4

Determine if distance and trajectory are safe.

Confirm that vehicle does not try to cut into lane.

6

Adjust speed if necessary.
Head and eye movements to view vehicle.

3

6.6.5 Continue accelerating up to speed.

Visually observe roadway.

3

Determine when traveling speed is reached.

2

Accelerate at necessary rate.
Head and eye movements for viewing.

3

6.6.6 Maintain safe lane position.

Visually observe roadway ahead.

1

Verify correct lane position.

1

Make necessary adjustments to steering.

1

6.6.7 Check surround for unsafe situations.

Scan for potential obstacles/hazards.

Listen for indications of unsafe situations.

7

Determine whether perceptual input indicates if current situation is safe/unsafe.

4

Head and eye movements for scanning.

1

6.6.8 Maintain safe distance from following vehicle at constant speed.

Visually assess distance and relative speed of following vehicle.

4

Determine if following-vehicle closing trajectory is safe.*

5

Increase acceleration if necessary.
Head and eye movements to observe rearview mirror.

3

* Difficulty in this subtask is increased by a value of 1 because of degraded information.

There are several noteworthy points for this segment. The first is that task 6.6.3 (check for hazards in turn path) is duplicated from the previous segment, which occurs shortly before. The reason it is repeated here is that in the previous segment this task was part of the criterion for deciding whether it was safe to turn, whereas here this task acts as a safety check for hazards. Also, while the subject vehicle is in the process of turning, it is necessary to check for right-traveling vehicles in the inside lane changing into the subject vehicle's lane (even though this is an illegal maneuver in an intersection in most jurisdictions), in case they may not have noticed or expected the subject vehicle's turn. On a similar note, there is no need to watch for conflicts with a lead vehicle in this segment because the lead vehicle would be pulling away with a faster relative speed; however, it is especially necessary, to check for conflicts with the following vehicle which will also, initially, be traveling at a faster relative speed. Finally, the estimated workload value for the cognitive element of task 6.6.8 was incremented by a value of 1, because determining the closing trajectory of the following vehicle is more difficult to do using the degraded indirect visual information from the rearview mirror.

Scenario 6, Segment 6 Diagram

View Alternative Text

Blue dotted outlines indicate general distribution of primary information in key perceptual tasks.

Note: Illustration dimensions and vehicle positions are not to scale.

Figure 52. Scenario 6–Right Turn on Red Light Execute Turn segment diagram.

 

Table 79. Scenario 6–Right Turn on Red Light Execute Turn segment of relative timing and duration of segment tasks and summary of key findings.

View Alternative Text

Potential contributions to high workload and information processing bottlenecks:

  • Concurrent and continuous conduct of 6.5.1 through 6.5.4 and 6.6.4 through 6.6.8.
  • Several of the tasks are forced-paced.
  • There is a high number of tasks overall.
  • The initial phase is a high-stress situation with possible severe consequences if conducted inaccurately.
Mitigating factors:
  • Most of the tasks are routine, automatic activities.

Task Pacing and Timing - Tasks 6.6.1 (accelerate to initiate turn), 6.6.2 (steer into turn), 6.7.5 (continue accelerating), and 6.6.6 (lane maintenance) are forced-paced because they are part of the ongoing task of driving. Task 6.6.3 (check for hazards in the turn path) is forced-paced because drivers only have a brief time to perform this task before the turn is complete.

In the task ordering, the tasks are mostly concurrent except for the division between the actual turn maneuver and getting up to speed once in the new lane. The one exception is task 6.6.4 (check for conflicts with vehicle in inside lane), which overlaps between the two groups of tasks because of the possibility that the inside-lane driver may be unaware of the subject vehicle and will try to change into the subject vehicle's lane.

Scenario-Wide Analysis

To help identify potential information processing bottlenecks in this scenario, workload estimates from all the segments were combined into a single scenario-wide workload profile that provides a general indication of where the areas of high workload demands are likely to be.

Figure 53 shows the summed workload estimates (separately for each information processing subtask) in each segment interval for the entire scenario. Also, the intervals in which key tasks are forced-paced are shaded in orange. As shown in figure 53, the workload peaks at moderate levels for both the perceptual and cognitive subtasks during the Stop, Prepare for Turn, and Execute Turn segments.

Figure 54, which displays the average workload estimate of all the tasks in play during a particular segment interval, shows that the peaks during the Stop segment in figure 53 arise from several tasks combined rather than just a few difficult tasks. In contrast, the peak during the Prepare for Turn segment arises from high average workload values. The elevated levels in the Execute Turn segment are likely due to a combination of both of these factors. Overall, average workload levels peak during the Approach segment for perceptual subtasks, and they peak during the Prepare for Turn and Execute Turn segments for both perceptual and cognitive subtasks.

View Alternative Text

Intervals containing nonroutine forced-paced tasks are shaded in orange. This graph shows the overall level of workload associated with a segment.

Figure 53. Scenario 6–Right Turn on Red Light total estimated workload ratings

for all tasks in each scenario segment.

View Alternative Text

Intervals containing nonroutine forced-paced tasks are shaded in orange. This graph generally represents the overall level of difficulty associated with the tasks in a segment.

Figure 54. Scenario 6–Right Turn on Red Light average estimated workload ratings

per task for each scenario segment.

Information Processing Bottlenecks

Information about the combined and average workload ratings, pacing of key tasks, and nature of bottlenecks for each segment is shown in table 80. Only information that represents potential problems is listed; blank cells indicate that no substantive issues occurred for a particular segment or cell. The table is followed by a list of key information processing bottlenecks identified in each of the segments.

Table 80. Scenario 6–Right Turn on Red Light combined and average

workload ratings, pacing of key tasks, and nature of bottlenecks that

indicate potential problems for each scenario segment.

Segment

Combined Workload

Average
Workload

Pacing of Key Tasks

Nature of Bottlenecks

Approach

 

 

 

Some perceptual tasks involving scanning or reading and cognitive tasks involve evaluation of multiple factors.

Prepare for Lane Change

 

High perceptual workload.

Forced-pacing of several key tasks.

Rapid sequence of some perceptual and cognitive tasks with moderate to high workload that involve distributed information and high time pressure.

Execute Lane Change

 

 

Forced-pacing of key tasks.

Concurrent and continuous conduct of tasks under high time pressure.

Stop

Moderate perceptual and cognitive workload.

 

Forced-pacing of some tasks.

A high number of tasks overall, with several concurrent tasks in the initial part involving moderate to high cognitive demands.

Prepare for Turn

Moderate perceptual and cognitive workload.

High perceptual and cognitive workload.

Forced-pacing of key tasks.

Concurrent and continuous conduct of some high-stress and demanding perceptual and cognitive subtasks under time pressure.
The information sources are widely distributed.

Execute Turn

Moderate perceptual and cognitive workload.

High perceptual and cognitive workload.

Forced-pacing of some key tasks.

Concurrent and continuous conduct of some high-stress and demanding perceptual and cognitive subtasks under time pressure.

Prepare for Lane Change nature of bottleneck: High time pressure:

  •   A few tasks involving moderate to high perceptual and cognitive workload focus on obtaining information from the environment in order to decide whether or not a lane change can be made. These tasks must be performed precisely and in rapid succession under high time pressure because the time available to make the decision is limited by the approaching intersection.

Execute Lane Change nature of bottleneck: High time pressure:

  •   Concurrent and ongoing perceptual and cognitive tasks with moderate to high workload are conducted under time pressure because the subject vehicle must safely get into the new lane with sufficient time to perform the Stop tasks. These effects are mitigated somewhat because most of these tasks are routine, automatic activities.

Stop nature of bottleneck: A relatively high number of concurrent tasks:

  •   Combined workload is high in the initial part for perceptual and cognitive subtasks because several tasks run concurrently, and some with moderate to high perceptual or cognitive workload. These effects are offset, however, by the self-pacing and routine, automatic nature of most of these tasks.

Prepare for Turn nature of bottleneck: Concurrent high workload, high-stress tasks under time pressure:

  • High combined and average perceptual and cognitive subtask workload involve continuous and concurrent tasks of moderate and high workload. These are also high-stress tasks that must be performed under time pressure, and they require information sampling that is widely distributed in the environment.

Execute Turn nature of bottleneck: Concurrent high workload, high-stress tasks under time pressure:

  • The initial phase of this segment is somewhat of a continuation of the previous segment. Moderate combined and high average perceptual and cognitive subtask workload involves continuous and concurrent tasks of moderate and high workload. In addition, these initial tasks are high stress and must be performed under time pressure.

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